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Omega General Help / Re: ABS-light constantly on after replacing front ABS/wheel speed sensors
« on: 30 October 2023, 12:00:41 »
Todays results from the Somerset 'elf-n-safety' conscious test labs....
The Markings on the sensor are 0265 001 220, which is the Bosch part number. The word Bosch is also molded into the rubber boot on the sensor.
I polished up the knuckle, and mounted the hub. Not torqued up to 300Nm, but tight enough for this. Then mounted it in the bench mill, with a bodged up drive assembly, and got it as centered as I could.
Then fired up the feeler gauges to measure the clearance...
The 0.8mm gauge goes in fine, the 0.9mm is snug, and the 1.0mm will not go in. So I'd say the installed clearance from sensor tip to reluctor ring is +/- 0.9mm (ish). I wouldn't argue or be worried about any value in the 0.8mm-1.0mm range though.
Then fire up the bench mill, and record the sensor waveforms on a cheap USB scope. The setup wasn't very well balanced, so I lost my bottle at 700Hz as the thing was shaking the desk and threatening to tip my cup of coffee over. Anyway...Scope traces at 100Hz, 200Hz, 400Hz and 700Hz.
Assuming standard tyres (235R45-17) with a rolling radius of 79.57 inches (2021mm), then these sensor frequencies equate to...
100Hz = 2.08 Rev/s = 165.5 inches/sec = 9.4 MPH
200Hz = 4.17 Rev/s = 331.0 inches/sec = 18.8 MPH
400Hz = 8.33 Rev/s = 662.0 inches/sec = 37.6 MPH
700Hz = 14.16 Rev/s = 1158.5 inches/sec = 65.8 MPH
As you can see, the sensor signal grows from about 140mV ptp at 100Hz (9.4MPH) to 630mV ptp at 700Hz (65 MPH). I'll leave you to extrapolate what happens at other speeds. The point is the output from the sensor is probably supposed to be of the order 100mV ptp at 5MPH, up to perhaps 1V ptp at 100MPH.
There will be quite a large tolerance in the ABS system to cope with mechanical and sensor variations - but these are the figures I can demonstrate.
Remember this is all Carlton gear. There is a possibility the Omega B is different. However, your "Holstein" sensors are producing significantly less signal voltage than these Bosch ones do (even at your reduced clearance), and I strongly suspect they are the cause of your issues.
The Markings on the sensor are 0265 001 220, which is the Bosch part number. The word Bosch is also molded into the rubber boot on the sensor.
I polished up the knuckle, and mounted the hub. Not torqued up to 300Nm, but tight enough for this. Then mounted it in the bench mill, with a bodged up drive assembly, and got it as centered as I could.
Then fired up the feeler gauges to measure the clearance...
The 0.8mm gauge goes in fine, the 0.9mm is snug, and the 1.0mm will not go in. So I'd say the installed clearance from sensor tip to reluctor ring is +/- 0.9mm (ish). I wouldn't argue or be worried about any value in the 0.8mm-1.0mm range though.
Then fire up the bench mill, and record the sensor waveforms on a cheap USB scope. The setup wasn't very well balanced, so I lost my bottle at 700Hz as the thing was shaking the desk and threatening to tip my cup of coffee over. Anyway...Scope traces at 100Hz, 200Hz, 400Hz and 700Hz.
Assuming standard tyres (235R45-17) with a rolling radius of 79.57 inches (2021mm), then these sensor frequencies equate to...
100Hz = 2.08 Rev/s = 165.5 inches/sec = 9.4 MPH
200Hz = 4.17 Rev/s = 331.0 inches/sec = 18.8 MPH
400Hz = 8.33 Rev/s = 662.0 inches/sec = 37.6 MPH
700Hz = 14.16 Rev/s = 1158.5 inches/sec = 65.8 MPH
As you can see, the sensor signal grows from about 140mV ptp at 100Hz (9.4MPH) to 630mV ptp at 700Hz (65 MPH). I'll leave you to extrapolate what happens at other speeds. The point is the output from the sensor is probably supposed to be of the order 100mV ptp at 5MPH, up to perhaps 1V ptp at 100MPH.
There will be quite a large tolerance in the ABS system to cope with mechanical and sensor variations - but these are the figures I can demonstrate.
Remember this is all Carlton gear. There is a possibility the Omega B is different. However, your "Holstein" sensors are producing significantly less signal voltage than these Bosch ones do (even at your reduced clearance), and I strongly suspect they are the cause of your issues.